Error Code P0356 is defined as Ignition Coil F Primary/Secondary Circuit Malfunction.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II tool, or vehicles made since 1996 up to present. Specifications on the definition, troubleshooting and repairs of course, vary from one make and/or model to another.


Coil on Plug (COP) are included in modern engines, and each cylinder comes equipped with a coil. The PCM (powertrain control module, also known as ECM or engine control module in other makes) is what controls the coil.

Putting the coil on top of the spark plug eliminates the need for sparkplug wires. This coil driver that connects to the PCM comes two wires: one for battery feed for power distribution center, and the other one for coil driver circuit from PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil. The PCM monitors the coil driver for faults.

For Error Code P0356, the problem means there’s an open or short detected in the driver circuit for coil number 6, or other issues in the ignition process of the coil pack. And depending on the vehicle, the PCM may also shut down the fuel injector to the cylinder.

Common Symptoms

The activation of the Check Engine light is one of the most obvious symptoms of this error code. Other symptoms affect the vehicle’s drivability, which include:

  • Engine misfire, can be both present or intermittent
  • Abnormal vibrations when idling or driving
  • Loss of acceleration

In some rare cases, the vehicle may not exhibit any symptoms at all.

Possible Causes

There are many reasons and contributory factors for vehicles to have this error code, and some of the possible causes are:

  • Faulty or corroded wiring of second cylinder coil pack
  • Faulty ignition coil(s)
  • Faulty spark plug(s)
  • Faulty idle air control valve or electronic body
  • Damaged or corrosion in the wiring that connects second cylinder coil pack to the PCM
  • Open or short in the wiring or electrical circuit of second cylinder coil pack
  • Carbon buildup causing blockage in the Throttle Body air passages
  • Intake manifold vacuum leaks
  • Faulty PCM (rare)

How to Check

To conduct a troubleshooting for this error code, technicians start by checking the suspected coil pack’s resistance through a resistance test.

Then, they will test the condition of the electrodes of the spark plug.

Next, they will measure the voltage present at the coil pack.

Then, they will inspect the wires that connect the coil packs for signs of corrosion, fraying and even melting.

Then, they check will check the coil pack circuit if it’s getting proper ground supply.

Next, they test the intake manifold for vacuum leaks.

Lastly, they measure the Hertz signal sent to the coil pack using multimeter. This step also helps them verify whether the PCM is sending the right signal to the coil pack.

How to Fix

Fixes for this error code are actually pretty simple and straightforward.

  • Repairing any forms of vacuum leaks such as leaks in the cracked vacuum line or intake manifold gasket
  • Replacing the coil pack
  • Replacing the spark plug
  • Repairing or replacing any damaged wiring in the coil pack
  • Replacing the PCM (rare)

Error Code P0356 is a fairly serious condition; for one, it presents plenty of drivability issues which expose users of the vehicle to safety risks. Second, misfires are always bad for the engine as it can cause damage or clogging to the catalytic converter. And in this case, the cylinders have to work twice as hard to run the vehicle, putting stress the cylinder and all involved components such as spark plugs, piston rings, and coil packs, causing them to wear faster.